Do hashtablez sampling on the first insertion into an empty SOO hashtable.
When sampling triggers, we skip SOO and allocate a backing array. We must do this because the HashtablezInfoHandle is part of the heap allocation (along with the control bytes and slots). By default, we sample 1 in ~1024 hashtables when sampling is enabled. This will impact performance because (a) we won't benefit from SOO so we would have worse data locality (more cache/TLB misses), and (b) the backing array capacity will be 3 instead of 1 so (b.1) we skip the rehash after the second insertion and (b.2) we potentially waste up to two slots worth of memory.
We also add an soo_capacity field to HashtablezInfo to allow for distinguishing which sampled tables may otherwise have been SOO - this will allow us to know approximately what fraction of tables are in SOO mode.
PiperOrigin-RevId: 617252334
Change-Id: Ib48b7a4870bd74ea3ba923ed8f350a3b75dbb7d3
diff --git a/absl/container/BUILD.bazel b/absl/container/BUILD.bazel
index 0de4526..c1df8d8 100644
--- a/absl/container/BUILD.bazel
+++ b/absl/container/BUILD.bazel
@@ -701,8 +701,10 @@
"//absl/base:config",
"//absl/base:core_headers",
"//absl/base:prefetch",
+ "//absl/functional:function_ref",
"//absl/hash",
"//absl/log",
+ "//absl/log:check",
"//absl/memory",
"//absl/meta:type_traits",
"//absl/strings",
diff --git a/absl/container/CMakeLists.txt b/absl/container/CMakeLists.txt
index 4b08e6a..7fa2e91 100644
--- a/absl/container/CMakeLists.txt
+++ b/absl/container/CMakeLists.txt
@@ -753,11 +753,13 @@
${ABSL_TEST_COPTS}
DEPS
absl::base
+ absl::check
absl::config
absl::container_memory
absl::core_headers
absl::flat_hash_map
absl::flat_hash_set
+ absl::function_ref
absl::hash
absl::hash_function_defaults
absl::hash_policy_testing
diff --git a/absl/container/internal/hashtablez_sampler.cc b/absl/container/internal/hashtablez_sampler.cc
index b21beef..e17ba14 100644
--- a/absl/container/internal/hashtablez_sampler.cc
+++ b/absl/container/internal/hashtablez_sampler.cc
@@ -18,13 +18,18 @@
#include <atomic>
#include <cassert>
#include <cmath>
+#include <cstddef>
+#include <cstdint>
#include <functional>
#include <limits>
#include "absl/base/attributes.h"
#include "absl/base/config.h"
+#include "absl/base/internal/per_thread_tls.h"
#include "absl/base/internal/raw_logging.h"
+#include "absl/base/macros.h"
#include "absl/base/no_destructor.h"
+#include "absl/base/optimization.h"
#include "absl/debugging/stacktrace.h"
#include "absl/memory/memory.h"
#include "absl/profiling/internal/exponential_biased.h"
@@ -73,7 +78,8 @@
HashtablezInfo::~HashtablezInfo() = default;
void HashtablezInfo::PrepareForSampling(int64_t stride,
- size_t inline_element_size_value) {
+ size_t inline_element_size_value,
+ uint16_t soo_capacity_value) {
capacity.store(0, std::memory_order_relaxed);
size.store(0, std::memory_order_relaxed);
num_erases.store(0, std::memory_order_relaxed);
@@ -93,6 +99,7 @@
depth = absl::GetStackTrace(stack, HashtablezInfo::kMaxStackDepth,
/* skip_count= */ 0);
inline_element_size = inline_element_size_value;
+ soo_capacity = soo_capacity_value;
}
static bool ShouldForceSampling() {
@@ -116,12 +123,12 @@
}
HashtablezInfo* SampleSlow(SamplingState& next_sample,
- size_t inline_element_size) {
+ size_t inline_element_size, uint16_t soo_capacity) {
if (ABSL_PREDICT_FALSE(ShouldForceSampling())) {
next_sample.next_sample = 1;
const int64_t old_stride = exchange(next_sample.sample_stride, 1);
- HashtablezInfo* result =
- GlobalHashtablezSampler().Register(old_stride, inline_element_size);
+ HashtablezInfo* result = GlobalHashtablezSampler().Register(
+ old_stride, inline_element_size, soo_capacity);
return result;
}
@@ -151,10 +158,11 @@
// that case.
if (first) {
if (ABSL_PREDICT_TRUE(--next_sample.next_sample > 0)) return nullptr;
- return SampleSlow(next_sample, inline_element_size);
+ return SampleSlow(next_sample, inline_element_size, soo_capacity);
}
- return GlobalHashtablezSampler().Register(old_stride, inline_element_size);
+ return GlobalHashtablezSampler().Register(old_stride, inline_element_size,
+ soo_capacity);
#endif
}
diff --git a/absl/container/internal/hashtablez_sampler.h b/absl/container/internal/hashtablez_sampler.h
index e41ee2d..4e11968 100644
--- a/absl/container/internal/hashtablez_sampler.h
+++ b/absl/container/internal/hashtablez_sampler.h
@@ -40,15 +40,20 @@
#define ABSL_CONTAINER_INTERNAL_HASHTABLEZ_SAMPLER_H_
#include <atomic>
+#include <cstddef>
+#include <cstdint>
#include <functional>
#include <memory>
#include <vector>
+#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/base/internal/per_thread_tls.h"
#include "absl/base/optimization.h"
+#include "absl/base/thread_annotations.h"
#include "absl/profiling/internal/sample_recorder.h"
#include "absl/synchronization/mutex.h"
+#include "absl/time/time.h"
#include "absl/utility/utility.h"
namespace absl {
@@ -67,7 +72,8 @@
// Puts the object into a clean state, fills in the logically `const` members,
// blocking for any readers that are currently sampling the object.
- void PrepareForSampling(int64_t stride, size_t inline_element_size_value)
+ void PrepareForSampling(int64_t stride, size_t inline_element_size_value,
+ uint16_t soo_capacity_value)
ABSL_EXCLUSIVE_LOCKS_REQUIRED(init_mu);
// These fields are mutated by the various Record* APIs and need to be
@@ -91,8 +97,13 @@
static constexpr int kMaxStackDepth = 64;
absl::Time create_time;
int32_t depth;
+ // The SOO capacity for this table in elements (not bytes). Note that sampled
+ // tables are never SOO because we need to store the infoz handle on the heap.
+ // Tables that would be SOO if not sampled should have: soo_capacity > 0 &&
+ // size <= soo_capacity && max_reserve <= soo_capacity.
+ uint16_t soo_capacity;
void* stack[kMaxStackDepth];
- size_t inline_element_size; // How big is the slot?
+ size_t inline_element_size; // How big is the slot in bytes?
};
void RecordRehashSlow(HashtablezInfo* info, size_t total_probe_length);
@@ -117,7 +128,7 @@
};
HashtablezInfo* SampleSlow(SamplingState& next_sample,
- size_t inline_element_size);
+ size_t inline_element_size, uint16_t soo_capacity);
void UnsampleSlow(HashtablezInfo* info);
#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
@@ -204,16 +215,16 @@
extern ABSL_PER_THREAD_TLS_KEYWORD SamplingState global_next_sample;
#endif // defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
-// Returns an RAII sampling handle that manages registration and unregistation
-// with the global sampler.
+// Returns a sampling handle.
inline HashtablezInfoHandle Sample(
- size_t inline_element_size ABSL_ATTRIBUTE_UNUSED) {
+ ABSL_ATTRIBUTE_UNUSED size_t inline_element_size,
+ ABSL_ATTRIBUTE_UNUSED uint16_t soo_capacity) {
#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
if (ABSL_PREDICT_TRUE(--global_next_sample.next_sample > 0)) {
return HashtablezInfoHandle(nullptr);
}
return HashtablezInfoHandle(
- SampleSlow(global_next_sample, inline_element_size));
+ SampleSlow(global_next_sample, inline_element_size, soo_capacity));
#else
return HashtablezInfoHandle(nullptr);
#endif // !ABSL_PER_THREAD_TLS
diff --git a/absl/container/internal/hashtablez_sampler_test.cc b/absl/container/internal/hashtablez_sampler_test.cc
index 8ebb08d..a80f530 100644
--- a/absl/container/internal/hashtablez_sampler_test.cc
+++ b/absl/container/internal/hashtablez_sampler_test.cc
@@ -15,8 +15,12 @@
#include "absl/container/internal/hashtablez_sampler.h"
#include <atomic>
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
#include <limits>
#include <random>
+#include <vector>
#include "gmock/gmock.h"
#include "gtest/gtest.h"
@@ -67,7 +71,7 @@
HashtablezInfo* Register(HashtablezSampler* s, size_t size) {
const int64_t test_stride = 123;
const size_t test_element_size = 17;
- auto* info = s->Register(test_stride, test_element_size);
+ auto* info = s->Register(test_stride, test_element_size, /*soo_capacity=*/0);
assert(info != nullptr);
info->size.store(size);
return info;
@@ -79,7 +83,8 @@
const size_t test_element_size = 17;
HashtablezInfo info;
absl::MutexLock l(&info.init_mu);
- info.PrepareForSampling(test_stride, test_element_size);
+ info.PrepareForSampling(test_stride, test_element_size,
+ /*soo_capacity_value=*/1);
EXPECT_EQ(info.capacity.load(), 0);
EXPECT_EQ(info.size.load(), 0);
@@ -94,6 +99,7 @@
EXPECT_GE(info.create_time, test_start);
EXPECT_EQ(info.weight, test_stride);
EXPECT_EQ(info.inline_element_size, test_element_size);
+ EXPECT_EQ(info.soo_capacity, 1);
info.capacity.store(1, std::memory_order_relaxed);
info.size.store(1, std::memory_order_relaxed);
@@ -106,7 +112,8 @@
info.max_reserve.store(1, std::memory_order_relaxed);
info.create_time = test_start - absl::Hours(20);
- info.PrepareForSampling(test_stride * 2, test_element_size);
+ info.PrepareForSampling(test_stride * 2, test_element_size,
+ /*soo_capacity_value=*/0);
EXPECT_EQ(info.capacity.load(), 0);
EXPECT_EQ(info.size.load(), 0);
EXPECT_EQ(info.num_erases.load(), 0);
@@ -120,6 +127,7 @@
EXPECT_EQ(info.weight, 2 * test_stride);
EXPECT_EQ(info.inline_element_size, test_element_size);
EXPECT_GE(info.create_time, test_start);
+ EXPECT_EQ(info.soo_capacity, 0);
}
TEST(HashtablezInfoTest, RecordStorageChanged) {
@@ -127,7 +135,8 @@
absl::MutexLock l(&info.init_mu);
const int64_t test_stride = 21;
const size_t test_element_size = 19;
- info.PrepareForSampling(test_stride, test_element_size);
+ info.PrepareForSampling(test_stride, test_element_size,
+ /*soo_capacity_value=*/0);
RecordStorageChangedSlow(&info, 17, 47);
EXPECT_EQ(info.size.load(), 17);
EXPECT_EQ(info.capacity.load(), 47);
@@ -141,7 +150,8 @@
absl::MutexLock l(&info.init_mu);
const int64_t test_stride = 25;
const size_t test_element_size = 23;
- info.PrepareForSampling(test_stride, test_element_size);
+ info.PrepareForSampling(test_stride, test_element_size,
+ /*soo_capacity_value=*/0);
EXPECT_EQ(info.max_probe_length.load(), 0);
RecordInsertSlow(&info, 0x0000FF00, 6 * kProbeLength);
EXPECT_EQ(info.max_probe_length.load(), 6);
@@ -165,7 +175,8 @@
const size_t test_element_size = 29;
HashtablezInfo info;
absl::MutexLock l(&info.init_mu);
- info.PrepareForSampling(test_stride, test_element_size);
+ info.PrepareForSampling(test_stride, test_element_size,
+ /*soo_capacity_value=*/1);
EXPECT_EQ(info.num_erases.load(), 0);
EXPECT_EQ(info.size.load(), 0);
RecordInsertSlow(&info, 0x0000FF00, 6 * kProbeLength);
@@ -174,6 +185,7 @@
EXPECT_EQ(info.size.load(), 0);
EXPECT_EQ(info.num_erases.load(), 1);
EXPECT_EQ(info.inline_element_size, test_element_size);
+ EXPECT_EQ(info.soo_capacity, 1);
}
TEST(HashtablezInfoTest, RecordRehash) {
@@ -181,7 +193,8 @@
const size_t test_element_size = 31;
HashtablezInfo info;
absl::MutexLock l(&info.init_mu);
- info.PrepareForSampling(test_stride, test_element_size);
+ info.PrepareForSampling(test_stride, test_element_size,
+ /*soo_capacity_value=*/0);
RecordInsertSlow(&info, 0x1, 0);
RecordInsertSlow(&info, 0x2, kProbeLength);
RecordInsertSlow(&info, 0x4, kProbeLength);
@@ -201,6 +214,7 @@
EXPECT_EQ(info.num_erases.load(), 0);
EXPECT_EQ(info.num_rehashes.load(), 1);
EXPECT_EQ(info.inline_element_size, test_element_size);
+ EXPECT_EQ(info.soo_capacity, 0);
}
TEST(HashtablezInfoTest, RecordReservation) {
@@ -208,7 +222,8 @@
absl::MutexLock l(&info.init_mu);
const int64_t test_stride = 35;
const size_t test_element_size = 33;
- info.PrepareForSampling(test_stride, test_element_size);
+ info.PrepareForSampling(test_stride, test_element_size,
+ /*soo_capacity_value=*/0);
RecordReservationSlow(&info, 3);
EXPECT_EQ(info.max_reserve.load(), 3);
@@ -229,7 +244,8 @@
for (int i = 0; i < 1000; ++i) {
SamplingState next_sample = {0, 0};
- HashtablezInfo* sample = SampleSlow(next_sample, test_element_size);
+ HashtablezInfo* sample = SampleSlow(next_sample, test_element_size,
+ /*soo_capacity=*/0);
EXPECT_GT(next_sample.next_sample, 0);
EXPECT_EQ(next_sample.next_sample, next_sample.sample_stride);
EXPECT_NE(sample, nullptr);
@@ -244,7 +260,8 @@
for (int i = 0; i < 1000; ++i) {
SamplingState next_sample = {0, 0};
- HashtablezInfo* sample = SampleSlow(next_sample, test_element_size);
+ HashtablezInfo* sample = SampleSlow(next_sample, test_element_size,
+ /*soo_capacity=*/0);
EXPECT_GT(next_sample.next_sample, 0);
EXPECT_EQ(next_sample.next_sample, next_sample.sample_stride);
EXPECT_NE(sample, nullptr);
@@ -260,7 +277,8 @@
int64_t total = 0;
double sample_rate = 0.0;
for (int i = 0; i < 1000000; ++i) {
- HashtablezInfoHandle h = Sample(test_element_size);
+ HashtablezInfoHandle h = Sample(test_element_size,
+ /*soo_capacity=*/0);
++total;
if (h.IsSampled()) {
++num_sampled;
@@ -275,7 +293,8 @@
auto& sampler = GlobalHashtablezSampler();
const int64_t test_stride = 41;
const size_t test_element_size = 39;
- HashtablezInfoHandle h(sampler.Register(test_stride, test_element_size));
+ HashtablezInfoHandle h(sampler.Register(test_stride, test_element_size,
+ /*soo_capacity=*/0));
auto* info = HashtablezInfoHandlePeer::GetInfo(&h);
info->hashes_bitwise_and.store(0x12345678, std::memory_order_relaxed);
@@ -358,11 +377,13 @@
std::vector<HashtablezInfo*> infoz;
while (!stop.HasBeenNotified()) {
if (infoz.empty()) {
- infoz.push_back(sampler.Register(sampling_stride, elt_size));
+ infoz.push_back(sampler.Register(sampling_stride, elt_size,
+ /*soo_capacity=*/0));
}
switch (std::uniform_int_distribution<>(0, 2)(gen)) {
case 0: {
- infoz.push_back(sampler.Register(sampling_stride, elt_size));
+ infoz.push_back(sampler.Register(sampling_stride, elt_size,
+ /*soo_capacity=*/0));
break;
}
case 1: {
diff --git a/absl/container/internal/raw_hash_set.h b/absl/container/internal/raw_hash_set.h
index 258458b..5818844 100644
--- a/absl/container/internal/raw_hash_set.h
+++ b/absl/container/internal/raw_hash_set.h
@@ -1775,17 +1775,48 @@
}
}
+template <typename CharAlloc>
+constexpr bool ShouldSampleHashtablezInfo() {
+ // Folks with custom allocators often make unwarranted assumptions about the
+ // behavior of their classes vis-a-vis trivial destructability and what
+ // calls they will or won't make. Avoid sampling for people with custom
+ // allocators to get us out of this mess. This is not a hard guarantee but
+ // a workaround while we plan the exact guarantee we want to provide.
+ return std::is_same<CharAlloc, std::allocator<char>>::value;
+}
+
+template <bool kSooEnabled>
+HashtablezInfoHandle SampleHashtablezInfo(size_t sizeof_slot,
+ size_t old_capacity, bool was_soo,
+ HashtablezInfoHandle forced_infoz,
+ CommonFields& c) {
+ if (forced_infoz.IsSampled()) return forced_infoz;
+ // In SOO, we sample on the first insertion so if this is an empty SOO case
+ // (e.g. when reserve is called), then we still need to sample.
+ if (kSooEnabled && was_soo && c.size() == 0) {
+ return Sample(sizeof_slot, SooCapacity());
+ }
+ // For non-SOO cases, we sample whenever the capacity is increasing from zero
+ // to non-zero.
+ if (!kSooEnabled && old_capacity == 0) {
+ return Sample(sizeof_slot, 0);
+ }
+ return c.infoz();
+}
+
// Helper class to perform resize of the hash set.
//
// It contains special optimizations for small group resizes.
// See GrowIntoSingleGroupShuffleControlBytes for details.
class HashSetResizeHelper {
public:
- explicit HashSetResizeHelper(CommonFields& c, bool was_soo, bool had_soo_slot)
+ explicit HashSetResizeHelper(CommonFields& c, bool was_soo, bool had_soo_slot,
+ HashtablezInfoHandle forced_infoz)
: old_capacity_(c.capacity()),
had_infoz_(c.has_infoz()),
was_soo_(was_soo),
- had_soo_slot_(had_soo_slot) {}
+ had_soo_slot_(had_soo_slot),
+ forced_infoz_(forced_infoz) {}
// Optimized for small groups version of `find_first_non_full`.
// Beneficial only right after calling `raw_hash_set::resize`.
@@ -1839,7 +1870,7 @@
// Reads `capacity` and updates all other fields based on the result of
// the allocation.
//
- // It also may do the folowing actions:
+ // It also may do the following actions:
// 1. initialize control bytes
// 2. initialize slots
// 3. deallocate old slots.
@@ -1869,26 +1900,15 @@
//
// Returns IsGrowingIntoSingleGroupApplicable result to avoid recomputation.
template <typename Alloc, size_t SizeOfSlot, bool TransferUsesMemcpy,
- size_t AlignOfSlot>
+ bool SooEnabled, size_t AlignOfSlot>
ABSL_ATTRIBUTE_NOINLINE bool InitializeSlots(CommonFields& c, Alloc alloc,
ctrl_t soo_slot_h2) {
assert(c.capacity());
- // Folks with custom allocators often make unwarranted assumptions about the
- // behavior of their classes vis-a-vis trivial destructability and what
- // calls they will or won't make. Avoid sampling for people with custom
- // allocators to get us out of this mess. This is not a hard guarantee but
- // a workaround while we plan the exact guarantee we want to provide.
- const size_t sample_size =
- (std::is_same<Alloc, std::allocator<char>>::value &&
- (was_soo_ || old_capacity_ == 0))
- ? SizeOfSlot
- : 0;
- // TODO(b/289225379): when SOO is enabled, we should still sample on first
- // insertion and if Sample is non-null, then we should force a heap
- // allocation. Note that we'll also have to force capacity of 3 so that
- // is_soo() still works.
HashtablezInfoHandle infoz =
- sample_size > 0 ? Sample(sample_size) : c.infoz();
+ ShouldSampleHashtablezInfo<Alloc>()
+ ? SampleHashtablezInfo<SooEnabled>(SizeOfSlot, old_capacity_,
+ was_soo_, forced_infoz_, c)
+ : HashtablezInfoHandle{};
const bool has_infoz = infoz.IsSampled();
RawHashSetLayout layout(c.capacity(), AlignOfSlot, has_infoz);
@@ -1904,12 +1924,13 @@
const bool grow_single_group =
IsGrowingIntoSingleGroupApplicable(old_capacity_, layout.capacity());
- if (was_soo_ && grow_single_group) {
+ if (SooEnabled && was_soo_ && grow_single_group) {
InitControlBytesAfterSoo(c.control(), soo_slot_h2, layout.capacity());
if (TransferUsesMemcpy && had_soo_slot_) {
TransferSlotAfterSoo(c, SizeOfSlot);
}
- } else if (old_capacity_ != 0 && grow_single_group) {
+ // SooEnabled implies that old_capacity_ != 0.
+ } else if ((SooEnabled || old_capacity_ != 0) && grow_single_group) {
if (TransferUsesMemcpy) {
GrowSizeIntoSingleGroupTransferable(c, SizeOfSlot);
DeallocateOld<AlignOfSlot>(alloc, SizeOfSlot);
@@ -1923,7 +1944,7 @@
c.set_has_infoz(has_infoz);
if (has_infoz) {
infoz.RecordStorageChanged(c.size(), layout.capacity());
- if (was_soo_ || grow_single_group || old_capacity_ == 0) {
+ if ((SooEnabled && was_soo_) || grow_single_group || old_capacity_ == 0) {
infoz.RecordRehash(0);
}
c.set_infoz(infoz);
@@ -2063,6 +2084,8 @@
bool had_infoz_;
bool was_soo_;
bool had_soo_slot_;
+ // Either null infoz or a pre-sampled forced infoz for SOO tables.
+ HashtablezInfoHandle forced_infoz_;
};
inline void PrepareInsertCommon(CommonFields& common) {
@@ -2545,6 +2568,8 @@
assert(size == 1);
common().set_full_soo();
emplace_at(soo_iterator(), *that.begin());
+ const HashtablezInfoHandle infoz = try_sample_soo();
+ if (infoz.IsSampled()) resize_with_soo_infoz(infoz);
return;
}
assert(!that.is_soo());
@@ -2682,8 +2707,7 @@
size_t size() const { return common().size(); }
size_t capacity() const {
const size_t cap = common().capacity();
- // Use local variables because compiler complains about using functions in
- // assume.
+ // Compiler complains when using functions in assume so use local variables.
ABSL_ATTRIBUTE_UNUSED static constexpr bool kEnabled = SooEnabled();
ABSL_ATTRIBUTE_UNUSED static constexpr size_t kCapacity = SooCapacity();
ABSL_ASSUME(!kEnabled || cap >= kCapacity);
@@ -3051,7 +3075,17 @@
SooEnabled());
return;
}
- if (SooEnabled() && size() <= SooCapacity()) {
+ if (fits_in_soo(size())) {
+ // When the table is already sampled, we keep it sampled.
+ if (infoz().IsSampled()) {
+ const size_t kInitialSampledCapacity = NextCapacity(SooCapacity());
+ if (capacity() > kInitialSampledCapacity) {
+ resize(kInitialSampledCapacity);
+ }
+ // This asserts that we didn't lose sampling coverage in `resize`.
+ assert(infoz().IsSampled());
+ return;
+ }
alignas(slot_type) unsigned char slot_space[sizeof(slot_type)];
slot_type* tmp_slot = to_slot(slot_space);
transfer(tmp_slot, begin().slot());
@@ -3322,6 +3356,15 @@
}
}
+ // Conditionally samples hashtablez for SOO tables. This should be called on
+ // insertion into an empty SOO table and in copy construction when the size
+ // can fit in SOO capacity.
+ inline HashtablezInfoHandle try_sample_soo() {
+ assert(is_soo());
+ if (!ShouldSampleHashtablezInfo<CharAlloc>()) return HashtablezInfoHandle{};
+ return Sample(sizeof(slot_type), SooCapacity());
+ }
+
inline void destroy_slots() {
assert(!is_soo());
if (PolicyTraits::template destroy_is_trivial<Alloc>()) return;
@@ -3374,7 +3417,20 @@
// HashSetResizeHelper::FindFirstNonFullAfterResize(
// common(), old_capacity, hash)
// can be called right after `resize`.
- ABSL_ATTRIBUTE_NOINLINE void resize(size_t new_capacity) {
+ void resize(size_t new_capacity) {
+ resize_impl(new_capacity, HashtablezInfoHandle{});
+ }
+
+ // As above, except that we also accept a pre-sampled, forced infoz for
+ // SOO tables, since they need to switch from SOO to heap in order to
+ // store the infoz.
+ void resize_with_soo_infoz(HashtablezInfoHandle forced_infoz) {
+ assert(forced_infoz.IsSampled());
+ resize_impl(NextCapacity(SooCapacity()), forced_infoz);
+ }
+
+ ABSL_ATTRIBUTE_NOINLINE void resize_impl(
+ size_t new_capacity, HashtablezInfoHandle forced_infoz) {
assert(IsValidCapacity(new_capacity));
assert(!fits_in_soo(new_capacity));
const bool was_soo = is_soo();
@@ -3382,7 +3438,8 @@
const ctrl_t soo_slot_h2 =
had_soo_slot ? static_cast<ctrl_t>(H2(hash_of(soo_slot())))
: ctrl_t::kEmpty;
- HashSetResizeHelper resize_helper(common(), was_soo, had_soo_slot);
+ HashSetResizeHelper resize_helper(common(), was_soo, had_soo_slot,
+ forced_infoz);
// Initialize HashSetResizeHelper::old_heap_or_soo_. We can't do this in
// HashSetResizeHelper constructor because it can't transfer slots when
// transfer_uses_memcpy is false.
@@ -3400,7 +3457,7 @@
const bool grow_single_group =
resize_helper.InitializeSlots<CharAlloc, sizeof(slot_type),
PolicyTraits::transfer_uses_memcpy(),
- alignof(slot_type)>(
+ SooEnabled(), alignof(slot_type)>(
common(), CharAlloc(alloc_ref()), soo_slot_h2);
// In the SooEnabled() case, capacity is never 0 so we don't check.
@@ -3621,26 +3678,29 @@
return move_elements_allocs_unequal(std::move(that));
}
- protected:
- // Attempts to find `key` in the table; if it isn't found, returns an iterator
- // where the value can be inserted into, with the control byte already set to
- // `key`'s H2. Returns a bool indicating whether an insertion can take place.
template <class K>
- std::pair<iterator, bool> find_or_prepare_insert(const K& key) {
- if (is_soo()) {
- if (empty()) {
+ std::pair<iterator, bool> find_or_prepare_insert_soo(const K& key) {
+ if (empty()) {
+ const HashtablezInfoHandle infoz = try_sample_soo();
+ if (infoz.IsSampled()) {
+ resize_with_soo_infoz(infoz);
+ } else {
common().set_full_soo();
return {soo_iterator(), true};
}
- if (PolicyTraits::apply(EqualElement<K>{key, eq_ref()},
- PolicyTraits::element(soo_slot()))) {
- return {soo_iterator(), false};
- }
+ } else if (PolicyTraits::apply(EqualElement<K>{key, eq_ref()},
+ PolicyTraits::element(soo_slot()))) {
+ return {soo_iterator(), false};
+ } else {
resize(NextCapacity(SooCapacity()));
- const size_t index =
- PrepareInsertAfterSoo(hash_ref()(key), sizeof(slot_type), common());
- return {iterator_at(index), true};
}
+ const size_t index =
+ PrepareInsertAfterSoo(hash_ref()(key), sizeof(slot_type), common());
+ return {iterator_at(index), true};
+ }
+
+ template <class K>
+ std::pair<iterator, bool> find_or_prepare_insert_non_soo(const K& key) {
prefetch_heap_block();
auto hash = hash_ref()(key);
auto seq = probe(common(), hash);
@@ -3660,6 +3720,16 @@
return {iterator_at(prepare_insert(hash)), true};
}
+ protected:
+ // Attempts to find `key` in the table; if it isn't found, returns an iterator
+ // where the value can be inserted into, with the control byte already set to
+ // `key`'s H2. Returns a bool indicating whether an insertion can take place.
+ template <class K>
+ std::pair<iterator, bool> find_or_prepare_insert(const K& key) {
+ if (is_soo()) return find_or_prepare_insert_soo(key);
+ return find_or_prepare_insert_non_soo(key);
+ }
+
// Given the hash of a value not currently in the table, finds the next
// viable slot index to insert it at.
//
@@ -3769,13 +3839,13 @@
return static_cast<slot_type*>(common().soo_data());
}
const slot_type* soo_slot() const {
- return reinterpret_cast<raw_hash_set*>(this)->soo_slot();
+ return const_cast<raw_hash_set*>(this)->soo_slot();
}
iterator soo_iterator() {
return {SooControl(), soo_slot(), common().generation_ptr()};
}
const_iterator soo_iterator() const {
- return reinterpret_cast<raw_hash_set*>(this)->soo_iterator();
+ return const_cast<raw_hash_set*>(this)->soo_iterator();
}
HashtablezInfoHandle infoz() {
assert(!is_soo());
diff --git a/absl/container/internal/raw_hash_set_test.cc b/absl/container/internal/raw_hash_set_test.cc
index 66baeb6..f00cef8 100644
--- a/absl/container/internal/raw_hash_set_test.cc
+++ b/absl/container/internal/raw_hash_set_test.cc
@@ -52,7 +52,9 @@
#include "absl/container/internal/hashtable_debug.h"
#include "absl/container/internal/hashtablez_sampler.h"
#include "absl/container/internal/test_allocator.h"
+#include "absl/functional/function_ref.h"
#include "absl/hash/hash.h"
+#include "absl/log/check.h"
#include "absl/log/log.h"
#include "absl/memory/memory.h"
#include "absl/meta/type_traits.h"
@@ -2035,6 +2037,9 @@
}
TYPED_TEST_P(SooTest, ReplacingDeletedSlotDoesNotRehash) {
+ // We need to disable hashtablez to avoid issues related to SOO and sampling.
+ SetHashtablezEnabled(false);
+
size_t n;
{
// Compute n such that n is the maximum number of elements before rehash.
@@ -2388,6 +2393,9 @@
// Verify that pointers are invalidated as soon as a second element is inserted.
// This prevents dependency on pointer stability on small tables.
TYPED_TEST_P(SooTest, UnstablePointers) {
+ // We need to disable hashtablez to avoid issues related to SOO and sampling.
+ SetHashtablezEnabled(false);
+
TypeParam table;
const auto addr = [&](int i) {
@@ -2523,7 +2531,7 @@
constexpr bool soo_enabled = std::is_same<SooIntTable, TypeParam>::value;
// Enable the feature even if the prod default is off.
SetHashtablezEnabled(true);
- SetHashtablezSampleParameter(100);
+ SetHashtablezSampleParameter(100); // Sample ~1% of tables.
auto& sampler = GlobalHashtablezSampler();
size_t start_size = 0;
@@ -2557,25 +2565,26 @@
absl::flat_hash_map<size_t, int> observed_checksums;
absl::flat_hash_map<ssize_t, int> reservations;
end_size += sampler.Iterate([&](const HashtablezInfo& info) {
- if (preexisting_info.count(&info) == 0) {
- observed_checksums[info.hashes_bitwise_xor.load(
- std::memory_order_relaxed)]++;
- reservations[info.max_reserve.load(std::memory_order_relaxed)]++;
- }
- EXPECT_EQ(info.inline_element_size, sizeof(typename TypeParam::value_type));
++end_size;
+ if (preexisting_info.contains(&info)) return;
+ observed_checksums[info.hashes_bitwise_xor.load(
+ std::memory_order_relaxed)]++;
+ reservations[info.max_reserve.load(std::memory_order_relaxed)]++;
+ EXPECT_EQ(info.inline_element_size, sizeof(typename TypeParam::value_type));
+
+ if (soo_enabled) {
+ EXPECT_EQ(info.soo_capacity, SooCapacity());
+ } else {
+ EXPECT_EQ(info.soo_capacity, 0);
+ }
});
+ // Expect that we sampled at the requested sampling rate of ~1%.
EXPECT_NEAR((end_size - start_size) / static_cast<double>(tables.size()),
0.01, 0.005);
- if (soo_enabled) {
- EXPECT_EQ(observed_checksums.size(), 9);
- } else {
- EXPECT_EQ(observed_checksums.size(), 5);
- for (const auto& [_, count] : observed_checksums) {
- EXPECT_NEAR((100 * count) / static_cast<double>(tables.size()), 0.2,
- 0.05);
- }
+ EXPECT_EQ(observed_checksums.size(), 5);
+ for (const auto& [_, count] : observed_checksums) {
+ EXPECT_NEAR((100 * count) / static_cast<double>(tables.size()), 0.2, 0.05);
}
EXPECT_EQ(reservations.size(), 10);
@@ -2591,12 +2600,141 @@
REGISTER_TYPED_TEST_SUITE_P(RawHashSamplerTest, Sample);
using RawHashSamplerTestTypes = ::testing::Types<SooIntTable, NonSooIntTable>;
INSTANTIATE_TYPED_TEST_SUITE_P(My, RawHashSamplerTest, RawHashSamplerTestTypes);
+
+std::vector<const HashtablezInfo*> SampleSooMutation(
+ absl::FunctionRef<void(SooIntTable&)> mutate_table) {
+ // Enable the feature even if the prod default is off.
+ SetHashtablezEnabled(true);
+ SetHashtablezSampleParameter(100); // Sample ~1% of tables.
+
+ auto& sampler = GlobalHashtablezSampler();
+ size_t start_size = 0;
+ absl::flat_hash_set<const HashtablezInfo*> preexisting_info;
+ start_size += sampler.Iterate([&](const HashtablezInfo& info) {
+ preexisting_info.insert(&info);
+ ++start_size;
+ });
+
+ std::vector<SooIntTable> tables;
+ for (int i = 0; i < 1000000; ++i) {
+ tables.emplace_back();
+ mutate_table(tables.back());
+ }
+ size_t end_size = 0;
+ std::vector<const HashtablezInfo*> infos;
+ end_size += sampler.Iterate([&](const HashtablezInfo& info) {
+ ++end_size;
+ if (preexisting_info.contains(&info)) return;
+ infos.push_back(&info);
+ });
+
+ // Expect that we sampled at the requested sampling rate of ~1%.
+ EXPECT_NEAR((end_size - start_size) / static_cast<double>(tables.size()),
+ 0.01, 0.005);
+ return infos;
+}
+
+TEST(RawHashSamplerTest, SooTableInsertToEmpty) {
+ if (SooIntTable().capacity() != SooCapacity()) {
+ CHECK_LT(sizeof(void*), 8) << "missing SOO coverage";
+ GTEST_SKIP() << "not SOO on this platform";
+ }
+ std::vector<const HashtablezInfo*> infos =
+ SampleSooMutation([](SooIntTable& t) { t.insert(1); });
+
+ for (const HashtablezInfo* info : infos) {
+ ASSERT_EQ(info->inline_element_size,
+ sizeof(typename SooIntTable::value_type));
+ ASSERT_EQ(info->soo_capacity, SooCapacity());
+ ASSERT_EQ(info->capacity, NextCapacity(SooCapacity()));
+ ASSERT_EQ(info->size, 1);
+ ASSERT_EQ(info->max_reserve, 0);
+ ASSERT_EQ(info->num_erases, 0);
+ ASSERT_EQ(info->max_probe_length, 0);
+ ASSERT_EQ(info->total_probe_length, 0);
+ }
+}
+
+TEST(RawHashSamplerTest, SooTableReserveToEmpty) {
+ if (SooIntTable().capacity() != SooCapacity()) {
+ CHECK_LT(sizeof(void*), 8) << "missing SOO coverage";
+ GTEST_SKIP() << "not SOO on this platform";
+ }
+ std::vector<const HashtablezInfo*> infos =
+ SampleSooMutation([](SooIntTable& t) { t.reserve(100); });
+
+ for (const HashtablezInfo* info : infos) {
+ ASSERT_EQ(info->inline_element_size,
+ sizeof(typename SooIntTable::value_type));
+ ASSERT_EQ(info->soo_capacity, SooCapacity());
+ ASSERT_GE(info->capacity, 100);
+ ASSERT_EQ(info->size, 0);
+ ASSERT_EQ(info->max_reserve, 100);
+ ASSERT_EQ(info->num_erases, 0);
+ ASSERT_EQ(info->max_probe_length, 0);
+ ASSERT_EQ(info->total_probe_length, 0);
+ }
+}
+
+// This tests that reserve on a full SOO table doesn't incorrectly result in new
+// (over-)sampling.
+TEST(RawHashSamplerTest, SooTableReserveToFullSoo) {
+ if (SooIntTable().capacity() != SooCapacity()) {
+ CHECK_LT(sizeof(void*), 8) << "missing SOO coverage";
+ GTEST_SKIP() << "not SOO on this platform";
+ }
+ std::vector<const HashtablezInfo*> infos =
+ SampleSooMutation([](SooIntTable& t) {
+ t.insert(1);
+ t.reserve(100);
+ });
+
+ for (const HashtablezInfo* info : infos) {
+ ASSERT_EQ(info->inline_element_size,
+ sizeof(typename SooIntTable::value_type));
+ ASSERT_EQ(info->soo_capacity, SooCapacity());
+ ASSERT_GE(info->capacity, 100);
+ ASSERT_EQ(info->size, 1);
+ ASSERT_EQ(info->max_reserve, 100);
+ ASSERT_EQ(info->num_erases, 0);
+ ASSERT_EQ(info->max_probe_length, 0);
+ ASSERT_EQ(info->total_probe_length, 0);
+ }
+}
+
+// This tests that rehash(0) on a sampled table with size that fits in SOO
+// doesn't incorrectly result in losing sampling.
+TEST(RawHashSamplerTest, SooTableRehashShrinkWhenSizeFitsInSoo) {
+ if (SooIntTable().capacity() != SooCapacity()) {
+ CHECK_LT(sizeof(void*), 8) << "missing SOO coverage";
+ GTEST_SKIP() << "not SOO on this platform";
+ }
+ std::vector<const HashtablezInfo*> infos =
+ SampleSooMutation([](SooIntTable& t) {
+ t.reserve(100);
+ t.insert(1);
+ EXPECT_GE(t.capacity(), 100);
+ t.rehash(0);
+ });
+
+ for (const HashtablezInfo* info : infos) {
+ ASSERT_EQ(info->inline_element_size,
+ sizeof(typename SooIntTable::value_type));
+ ASSERT_EQ(info->soo_capacity, SooCapacity());
+ ASSERT_EQ(info->capacity, NextCapacity(SooCapacity()));
+ ASSERT_EQ(info->size, 1);
+ ASSERT_EQ(info->max_reserve, 100);
+ ASSERT_EQ(info->num_erases, 0);
+ ASSERT_EQ(info->max_probe_length, 0);
+ ASSERT_EQ(info->total_probe_length, 0);
+ }
+}
#endif // ABSL_INTERNAL_HASHTABLEZ_SAMPLE
TEST(RawHashSamplerTest, DoNotSampleCustomAllocators) {
// Enable the feature even if the prod default is off.
SetHashtablezEnabled(true);
- SetHashtablezSampleParameter(100);
+ SetHashtablezSampleParameter(100); // Sample ~1% of tables.
auto& sampler = GlobalHashtablezSampler();
size_t start_size = 0;
@@ -2974,7 +3112,7 @@
bool frozen = true;
TypeParam t{FreezableAlloc<typename TypeParam::value_type>(&frozen)};
if (t.capacity() != SooCapacity()) {
- EXPECT_LT(sizeof(void*), 8);
+ CHECK_LT(sizeof(void*), 8) << "missing SOO coverage";
GTEST_SKIP() << "not SOO on this platform";
}
@@ -3006,14 +3144,18 @@
FreezableSizedValueSooTable<16>>;
INSTANTIATE_TYPED_TEST_SUITE_P(My, SooTable, FreezableSooTableTypes);
-TEST(Table, RehashToSoo) {
+TEST(Table, RehashToSooUnsampled) {
SooIntTable t;
if (t.capacity() != SooCapacity()) {
- EXPECT_LT(sizeof(void*), 8);
+ CHECK_LT(sizeof(void*), 8) << "missing SOO coverage";
GTEST_SKIP() << "not SOO on this platform";
}
- t.reserve(10);
+ // We disable hashtablez sampling for this test to ensure that the table isn't
+ // sampled. When the table is sampled, it won't rehash down to SOO.
+ SetHashtablezEnabled(false);
+
+ t.reserve(100);
t.insert(0);
EXPECT_EQ(*t.begin(), 0);
@@ -3026,7 +3168,7 @@
EXPECT_EQ(t.find(1), t.end());
}
-TEST(Table, ResizeToNonSoo) {
+TEST(Table, ReserveToNonSoo) {
for (int reserve_capacity : {8, 100000}) {
SooIntTable t;
t.insert(0);
